Particulate rare earth element behavior in the North Atlantic (GEOVIDE cruise)

Marion Lagarde,Pascale Lherminier,Hélène Planquette,Catherine Jeandel,Nolwenn Lemaitre,Moustafa Belhadj,Mélanie Grenier

doi:10.5194/bg-17-5539-2020

Abstract

Abstract. Particulate concentrations of the 14 Rare Earth Elements (PREE), yttrium, and 232-thorium were measured in 200 samples collected in the epipelagic (ca. 0–200 m) and mesopelagic (ca. 200–1500 m) zones of the North Atlantic during the GEOVIDE cruise (May/June 2014, R/V Pourquoi Pas?, GEOTRACES GA01), providing the most detailed snapshot of the PREE distribution in the North Atlantic so far. Concentrations of particulate cerium (PCe) varied between 0.2 and 16 pmol L−1, while particulate neodymium (PNd) concentrations ranged between 0.1 and 6.1 pmol L−1. Particulate ytterbium (PYb) concentrations ranged between 0.01 and 0.50 pmol L−1. In addition, this study showed that PREE distributions were also controlled by the biological production in the upper sunlit ocean and by remineralization processes in the mesopelagic area. Low surface concentrations combined with normalized PREE patterns displaying a negative Ce anomaly and HREE enrichments pointed to freshly formed biogenic particles imprinting the seawater signature. A significant relationship between biogenic silica (BSi) and PHREE was also observed in the Labrador and Irminger seas, due to the occurrence of strong diatom blooms at the sampling time. In order to identify dissolved-particulate processes independent of the ionic radius, we used PHo∕PY ratios and showed that absorption processes were predominant in the upper ocean, while adsorption processes dominated at deeper depths. This study highlighted different lithogenic fractions of PREE and dispersion depending on the shelf: off the Iberian margin, up to 100 % of the PREE were determined to have a lithogenic origin. This lithogenic input spread westward along an intermediate nepheloid layer (INL), following isopycnals up to 1700 km away from the margin. In contrast, along the Greenland and Newfoundland margins, the circulation maintained lithogenic inputs of PREE along the coasts.

Highlights

Particles and water mass circulation are the main vectors in transferring chemical species from the surface to the deep ocean (Gehlen et al, 2006; Kwon et al, 2009; Lam and Marchal, 2015; Ohnemus and Lam, 2015)
We present the first basin-scale section of PREE concentrations and fractionation patterns in suspended particles collected in the subpolar North Atlantic (SPNA), along the GEOVIDE section, from the surface to 1500 m depth
In Tervuren, an inductively coupled plasma quadrupole mass spectrometer (ICP-QMS; X Series 2 Thermo Fischer®) was used, while a high-resolution mass spectrometer was used in Toulouse (HR-ICP-MS; Element XR Thermo Fischer®)

Summary

Introduction

Particles and water mass circulation are the main vectors in transferring chemical species from the surface to the deep ocean (Gehlen et al, 2006; Kwon et al, 2009; Lam and Marchal, 2015; Ohnemus and Lam, 2015). Particles are usually divided in two classes: large sinking particles that dominate the vertical flux, and small particles that are in suspension in the water column. These small suspended particles represent over 80 % of the total particle mass (Lam et al, 2015, and references therein). Their higher surface to volume ratios make suspended particles the main drivers of dissolved-particulate exchanges (Crecelius, 1980; Trull and Armand, 2001). In the subpolar North Atlantic, particulate iron (PFe)

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